Devices and systems for delivering an agent to the skin of a subject comprise an anhydrous agent (e.g. a pharmaceutical agent or a cosmetic agent), and an anhydrous heating component and a reservoir containing a solvent. When in use solvent released from the reservoir hydrates the anhydrous agent to produce a solution and hydrates the anhydrous heating component which reacts exothermically thereby heating the solution. The devices and systems enable the transdermal delivery of pharmaceutical and cosmetic agents.
